This invention relates generally to techniques for testing soil.
It is often important to determine properties such as the resistance of soil to liquefaction, the degradation characteristics of soil, the shear modulus of soil at low levels of shear deformation, and the variation in shear modulus of soil with shear deformation. Commonly, these soil properties, as well as others, are necessary for analyses which predict the response of a site or foundation structure system to dynamic loading caused by earthquakes, ocean waves, or mechanical vibrations.
Soil properties may be determined by in situ field tests. For example, the liquefaction resistance of the soil may be determined by penetration tests that involve penetrating a closed-ended probe into the ground at a slow, controlled rate or driving a cylinder into the ground by violent impacts. The resistance of the soil to liquefaction is correlated to the resistance of the probe or cylinder during penetration.
A technique that can measure the resistance to liquefaction by torsionally exciting the soil is disclosed in U.S. Pat. Nos. 4,594,899 and 5,203,824 to Robert and Wanda Henke. In these patents, the illustrated testing device includes a pair of concentric open-ended cylinders that are inserted into the soil to be tested. A torque may be applied to the inner cylinder and the response of the cylinder in the soil to the applied torque may be measured by sensors mounted on the inner cylinder.
In such soil tests, a borehole is drilled to access a soil sample and the testing device is lowered down the borehole to test the soil. The testing device may be secured to an auger in the borehole. The testing device may be subjected to substantial applied forces or torques or other reaction forces from the soil. Thus, the auger to which the testing device is anchored may serve as a reaction means to carry out various operations on the testing device.
A soil testing assembly includes a soil testing cylinder and a housing. An extractor rod connects the testing cylinder and the housing while allowing relative axial movement between the rod, the housing and the testing cylinder.